1. The field of art to which the invention pertains includes the art of measuring and testing as directed to fluid pressure gauges.
2. Gauge instruments, and particularly pressure gauges or the like, have been widely used and are commercially available from a variety of manufacturing sources. Being that such pressure gauges enjoy very extensive commercial and industrial use, they are supplied by a plurality of manufacturers, and are regarded as high production items. Because they are sold in very price-conscious competition, each manufacturer instinctively strives to reduce product costs by improvements, however marginal, which reduce labor and/or materials that can contribute to cost savings in the end product.
All pressure gauges include a socket by which the gauge can be connected to a source of fluid pressure to be measured. In a typical construction, the gauge socket may be formed of bar stock of square or hexagonal cross-section whereby the unmachined surface can serve as wrench flats during installation and removal of the gauge. Despite the foregoing virtue of the square or hex section, it is highly desirable, and indeed preferable, to make the socket from round stock, i.e., of circular cross-section. Generally speaking, the advantages of the latter are threefold, namely: (a) for a given size, round stock is the most economical bar shape; (b) round stock geometry facilitates joining of the case and socket when welding or brazing is the method of choice; and (c) a round interface between socket and case facilitates sealing whether it be a metallurgical bond or mechanical seal.
When the socket is fabricated from round stock, it is common practice to mill or broach two parallel flats as wrenching surfaces. This metal removal, of course, reduces the distance across the wrench flats to a dimension substantially less than basic stock diameter with a dimension across the wrench flats less than the major diameter of the socket thread. As a consequence, the amount of torque that can be applied, for example, to a 7/8-inch diameter socket with 5/8-inch parallel flats without stripping the wrench flats is reduced substantially compared to other sockets from larger square or hex stock. While the machined, parallel flats generally offer sufficient strength for making up the process connection, some code standards, such as the German DIN standard No. 16288, require that the wrenching surface be square or hexagonal and of a size larger than the major thread diameter of the socket.
Needless to say, utilizing oversized bar stock of square or hexagonal cross section merely to accommodate the foregoing standard not only constitutes a waste in both labor and material, but at the same time it defeats the noted virtues for the use of round stock mentioned above. Despite recognition of the problem, a solution therefor has not heretofore been known.